Photovolataic array module design for solar electric power generation systems

ABSTRACT

The invention relates to a solar photovoltaic array module design, which constitutes three steps of optical concentrations of photovoltaic electric power generation systems. A compound parabolic concentrator (CPC) is mounted under a first optical concentrating fresnel lens that concentrates the intensity of sunlight to five times above normal level. Then the focused sunlight is further concentrated twenty times by the second optical concentrator CPC. The high mirror quality of CPC allows 98% of the reflected rays to be focused at the bottom of the CPC. At this point, the intensified sunlight passes through a third optical concentrator glass lens, which with anti-reflection coating on the top of the glass lens&#39; surface, incident on the multi-junction solar cell accomplish the third optical concentration for the photovoltaic electric energy conversion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a thin film multi-junction photovoltaicarray module of solar electric power systems.

[0003] 2. The Prior Art

[0004] U.S. Pat. No. 5,505,789 to Fraas et al discloses a line-focusphotovoltaic module using solid optical secondaries for improvedradiation resistance. This invention consists of an array of lineararched fresnel lenses with a linear photovoltaic cell receiver locatedalong the focal line of each lens. The optical secondaries may beparabolic in shape.

[0005] These systems disclose the combination of fresnel lenses, andparabolic reflectors. U.S. patent application Ser. No. 09/687,960discloses a combination of a fresnel lens, compound parabolic reflectorincorporated with third optical concentration glass lenses andmulti-junction solar cells for photovoltaic electric energy conversion.

SUMMARY OF THE INVENTION

[0006] The invention relates to a thin film multi-junction photovoltaicarray module of solar electric power generation systems. The highperformance photovoltaic (PV) array module with multi-junctionconcentrator solar cells converts directly 30 or 40% of received solarenergy to electricity.

[0007] A photovoltaic solar cell is a semiconductor device that convertssunlight directly to electricity through the Photovoltaic Effect. One ofthe important developments of PV applications is the lowering of thesystem cost through the design of the PV array module to moreefficiently convert the sunlight directly to electricity.

[0008] The PV array module contains multi-step concentrations ofsunlight with Fresnel lenses, CPC reflectors and specially shaped glasslenses that can be made with much smaller surface areas of expensivemulti-junction concentrator solar cells in the system. Solarhigh-concentration and high-efficiency multi-junction solar cells arethe essential factors for lowering the cost of PV array modules whichproduce electricity.

[0009] To meet the requirement of ultra high efficiency, concentratorsolar cells, such as tandem GaInP/GaInAs and other multi-junctionconcentrator solar cells, are provided to generate more than 32 or 45%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Other objects and features of the present invention will becomeapparent from the following detailed description considered inconnection with the accompanying drawings. It is to be understood,however, that the drawings are designed as an illustration only and notas a definition of the limits of the invention.

[0011] In the drawings, wherein similar reference characters denotesimilar elements throughout the several views:

[0012]FIG. 1a shows a photovoltaic array module.

[0013]FIG. 1b shows a sunlight concentrator system of the solarphotovoltaic array shown on FIG. 1a.

[0014]FIG. 1c shows a cross sectional view through A-A of FIG. 1b;

[0015]FIG. 2a shows the sunlight concentrator of FIG. 1b having aphotovoltaic thin film multi-junction concentrator solar cell;

[0016]FIG. 2b shows a sectional view through B-B of FIG. 2a;

[0017]FIG. 3a shows another embodiment of a sunlight concentrator havingan optical fiber and a photovoltaic concentrator cell; and

[0018]FIG. 3b shows a sectional view through C-C of FIG. 3a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] Referring to the drawings and in particular to FIGS. 1a and 1 b,a sunlight concentrator 10 is shown containing first opticalconcentrator 12 for focusing sunrays five times their normal intensity.Second optical concentrator 14 is disposed below first opticalconcentrator 12. Second optical concentrator 14 concentrates the focusedsunrays twenty times. Third optical concentrator 20, being a speciallyshaped glass lens, is disposed at the bottom of second opticalconcentrator 14. Concentrator solar cell 22 is disposed below thirdoptical concentrator 20. Third optical concentrator 20 focuses the raysup to 1000 times of the original solar isolation. In addition, solarcell 22 can provide a 45% conversion efficiency. Fluid flows throughheat dissipater 16 and is heated by solar cells 22.

[0020] In a preferred embodiment, solar cells 22 comprise a TandemGaInP/GaInAs or GaAs concentrator solar cells. Also in a preferredembodiment, first optical concentrator 12 is a fresnel lens and secondoptical concentrator 14 is a compound parabolic concentrator. Thirdoptical concentrator 20 is an optical concentrating glass lens, havingone of three different possible shapes for suitable differentapplications.

[0021] Second optical concentrator 14 is made of glass-mirror containinga reflective surface coating and several layers of protective materials.The reflective surface coating can also be aluminum foil or a chromecoated metal plate.

[0022] Second optical concentrator 14 can be made of a ceramic materialhaving a glass-mirror with a silver-reflective coating covered withseveral layers of protective materials. The ceramic pad is used to mountsecond optical concentrator 14 to the concentrator structure with aspecial adhesive. The protective materials reduce the thermal stress athigh operating temperatures.

[0023] In another embodiment shown in FIGS. 2a and 2 b, solar cell 22comprises a photovoltaic thin film multi-junction concentrator cell. InFIGS. 3a and 3 b, sunlight concentrator 10 contains first opticalconcentrator 12, second optical concentrator 14, third opticalconcentrator 20 and an optical fiber 30. Photovoltaic concentrator cell22 is disposed below optical fiber 30. In FIG. 3b, the third opticalconcentrator 20 is a glass lens with an anti-reflection coating,connected to an optical fiber 30 with diameter less than 3 mm above thehigh efficiency multi-junction concentrator solar cells 22 with aconcentration rate of 500 times of normal sun rays.

[0024] The function of the device can be described as follows:

[0025] The focused sunlight from the first optical concentration 12 withthe scope of the incoming sunrays passes through the wider openingaperture (upward opening) of the second optical concentration 14, namelythe compound parabolic concentration (CPC). Hence, a margin around thecircle of rays allows the maximum amount of sunlight possible to beconcentrated even if the tracking mechanism does not function preciselyand the parabolic concentration is not positioned perpendicularly to thesun. The focused sunlight is continuously reflected by the CPC mirrorand is again refocused at the bottom of the CPC as a three-dimensionalring of light resembling a donut.

[0026] To further harmonize and concentrate the ring of light, threedifferent shapes of solid glass lenses (one with optical fibers) may beused as the third optical concentrator 20.

[0027] First, as in FIG. 1c, the glass lens, situated at the bottom ofthe second optical concentrator 14, may have a bra-shaped cross-section.The cross section view of the focused light resembles two crab eyeslocated at both sides of the base of the cross section view of the CPC.The cross section of the glass lens is used to harmonize the ring oflight and to concentrate that light to one thousand times that of normalincoming sunlight intensity after fresnel and CPC lenses. That lightthen impinges on the multi-junction concentrator solar cells. Thebra-shaped lens is coated with an anti-reflective coating.

[0028] Second, as shown in FIG. 2b, where solar cells require fewerdegrees of concentration, the crescent-shaped glass lens can be used asthe third optical concentrator 20. This glass lens has a cross-sectionresembling a crescent. The lens has a convex, upward facing surfacehaving a greater curvature than that of the concave, downward-facingsurface. The lens is also coated with an anti-reflective coating.

[0029] Third, as shown in FIG. 3b, a half-sphere-shaped small piecedsolid glass lens, which has convex upward-facing surface and a flatdownward-facing surface, may be used. It is connected to a short length(less than three diameters, with D<3 mm) of optical fiber. At the bottomof the optical fiber, the focused light passes the fiber and impinges onthe concentrator multi-junction solar cells 22. The lens is also coatedwith anti-reflective coating.

[0030] Accordingly, while only a few embodiments of the presentinvention have been shown and described, it is obvious that many changesand modifications may be made thereunto without departing from thespirit and scope of the invention.

What is claimed is:
 1. A solar photovoltaic array module of electricpower generation system for residential homes comprising: a firstoptical concentrator, for focusing sun rays such that the rays areconcentrated five times their normal intensity; a second opticalconcentrator having a bottom side and being disposed under said firstoptical concentrator for further concentration of the focused sun raystwenty times; a third optical concentrator, having an upward anddownward facing surface, disposed at said bottom side of said secondoptical concentrator for further concentration of the focused sun rays;a concentrator solar cell disposed below said third optical concentratorto generate a higher electric conversion efficiency; and a set of finsbelow the solar cell substrate disposed on said bottom side of saidsolar cells.
 2. The system according to claim 1, wherein said firstoptical concentrator comprises a fresnel lens.
 3. The system accordingto claim 1, wherein said second optical concentrator comprises acompound parabolic concentrator.
 4. The system according to claim 3,wherein said compound parabolic concentrator is made of glass.
 5. Thesystem according to claim 3, wherein said compound parabolicconcentrator is made of ceramic.
 6. The system according to claim 3,wherein said compound parabolic concentrator comprises a reflectivecoating surface and protective coatings.
 7. The system according toclaim 6, wherein said reflective coating surface is aluminum.
 8. Thesystem according to claim 6, wherein said reflective coating surface ischrome plated on metal plates.
 9. The system according to claim 1,wherein said third optical concentrator comprises an opticalconcentrator glass lens.
 10. The system according to claim 9, whereinsaid optical concentration glass lens has a bra-shaped cross section.11. The system according to claim 9, wherein said optical concentratorglass lens has a convex upward facing surface and a concave downwardfacing surface of less curvature forming a crescent cross section. 12.The system according to claim 9, wherein said optical concentrator glasslens has a convex upward facing surface and a flat downward facingsurface, connecting to an optical fiber.
 13. The system according toclaim 9, wherein said concentration glass lenses are selected for thegroup consisting of tandem GaInP/GaInAs cell and GaAs cell.
 14. Thesystem according to claim 9, wherein said concentrator glass lenses areselected for photovoltaic thin film multi-junction cells.
 15. A solarphotovoltaic array module of an electric power generation system forresidential homes comprising: a fresnel lens for focusing sun rays suchthat the rays are concentrated five to ten times their normal intensity;a compound parabolic concentrator having a bottom side and beingdisposed under said fresnel lens for further concentration of saidfocused sun rays twenty to fifty times; an optical fiber disposed atsaid bottom of the compound parabolic concentrator; and a photovoltaicconcentrator solar cell disposed below the optical concentration glasslens for creating a higher conversion efficiency.
 16. The systemaccording to claim 15, wherein said compound parabolic concentrator ismade of glass mirror.
 17. The system according to claim 15, wherein saidcompound parabolic concentrator is made of ceramic.
 18. The systemaccording to claim 15, wherein said compound parabolic concentratorcomprises a reflective coating surface and protective coatings.
 19. Thesystem according to claim 15, wherein said reflective coating surface ischrome plated on metal plates.